The release of TGF-β1 by live DC upon apoptotic DC uptake was regulated at the translational level, as no upregulation of TGF-β1 mRNA was observed. In order to investigate the underlying mechanism, we looked at the role of the mammalian target of rapamycin

(mTOR). mTOR, a serine/threonine protein kinase, is a regulator of translation and its major substrates this website include p70S60K serine/threonine kinase and 4E-binding protein (4EBP-1). Live DC were co-cultured with apoptotic DC in the presence of rapamycin, a known inhibitor of mTOR pathway. Next, we looked at the levels of total and active TGF-β1 released in the media (Fig. 8A). Our findings indicate that pre-treatment with rapamycin resulted in significant reduction of both total and active TGF-β1 released in media, indicating a role of mTOR in the observed TGF-β1 release upon uptake of apoptotic DC by viable DC.

Furthermore, TGF-β1 secretion in response to LPS stimulation of viable DC that Metformin had taken apoptotic DC was also suppressed in the presence of rapamycin (Fig. 8B). Taken together, our results show that the impact of dying DC on the immune system is dependent on the manner in which DC die. If DC undergo apoptosis and viable DC take them up, then viable DC transform into tolerogenic DC. These tolerogenic Carnitine dehydrogenase DC are resistant to stimuli-induced maturation, secrete TGF-β1, which is dependent on mTOR pathway and induce generation of Foxp3+ Treg. Surprisingly, our findings show that necrotic DC, irrespective of their maturation status are not immunostimulatory, which may be due to the paucity of the presence of certain immunosuppressive factors in primary DC, rendering them

non-immunogenic even after the cellular contents are released into the extracellular milieu. However, such factors still need to be identified. Studies have shown that DC can take up antigen from dying cells and cross-present the antigenic material onto both MHC I and MHC II 20, 21. However, these studies relied on the use of mature DC to phagocytose apoptotic cells. We can speculate that perhaps in a physiological setting, if the causative agent of DC apoptosis is an infection, then it is usually the semi-mature or mature viable DC in close proximity that take up apoptotic DC. Thereby, these viable DC can cross-present the antigen and then prime a T-cell response rather than induction of tolerance, as seen in our study. Previous studies have indicated that phosphatidylserine, an anionic aminophospholipid, which is exposed to cell surface as cells undergo apoptosis, plays an important role in the recognition and clearance of apoptotic cells by macrophages.